Weight Machines vs. Free Weights

I have a friend who thinks I have some philosophical aversion to strength training. Although I do choose to run as my daily workout, I keep promising her that I will one day incorporate some upper body strength training. The funny thing is that I really have no aversion, philosophical or otherwise, to strength training. Muscle physiology has always been a huge area of interest for me. I love talking about Huxley’s cross-bridge theory and hypertrophy and force-length and force-velocity properties of muscle. I’ve had the honor of studying muscle under Dr. Walter Herzog, one of the best biomechanists in the world, whom I owe a lot to. For my master’s thesis a long time ago, I studied motor unit recruitment during eccentric contractions. I gave my experimental subjects electrical shocks as they did leg extensions. Fun stuff. Those were the days…

Anyway, thinking about strength training brought me back to this article I wrote a while back about machines vs. free weights, so I figured I would share it with you as I inch closer to doing some strength training myself.

With all the different types of strength training equipment and exercises, how do you know which to use for the best results? Both machines and free weights have their advantages and disadvantages. So which type of equipment is better? Here’s the tale of the tape:



Weight Machines: Weight machines use variable resistance, changing resistance throughout the range of motion. To accomplish this, weight machines have geometrically-shaped cams integrated with a pulley system that change the length of the lever arm of the external weight (the perpendicular distance from the weight to the machine’s axis of rotation). The cams are shaped such that, at weaker joint positions, the lever arm of the external weight is shorter, making it easier for you to lift the weight. At stronger joint positions, the lever arm of the external weight is longer, making it more difficult to lift the weight. Manipulating the lever arms through which the external weight is applied allows weight machines to place more stress on the muscles at the angles at which they are capable of producing greater forces. However, given the differences between the length of people’s limbs and their ability to produce force at different joint angles, not all machines may be able to match their resistance to your strength.

Free Weights: With free weights, the resistance on the muscle remains constant throughout the joint’s range of motion. When you lift a five-pound dumbbell, it is five pounds at all parts of the lift—beginning, middle, and end. Since there are points in your joints’ ranges of motion at which your muscles are stronger and points at which they are weaker, and the amount of weight you can lift is limited by the weakest point, free weights only serve as a strong enough training stimulus for those weaker joint positions.

Advantage: Weight Machines

 Movement Specificity

Weight Machines: Most weight machines allow only single-joint exercises with movement occurring in a single plane. Since weight machines guide your movement, they do not recruit muscles other than those specifically targeted by the machine. This apparent lack of freedom does confer one advantage—weight machines allow you to isolate specific muscles or parts of muscles, which is valuable if you want to shape a specific body part.  

Free Weights: Movements using free weights occur in three dimensions. The added task of balancing free weights in the three-dimensional plane recruits other ancillary muscles. However, the greater instability of free weights may require the need for a spotter, which would not be necessary when using weight machines. In contrast to weight machines, free weights allow you to perform multi-joint exercises and therefore more closely mimic the activities of daily life and other specific activities for which you may want to train. Multi-joint movements also confer greater neural benefits in terms of acquiring specific skills. While multi-joint, free-weight exercises require a higher level of skill and may take some time to learn, this slight disadvantage is more than compensated for by the gains in movement specificity.

Advantage: Free Weights

 Strength Gains

            Weight Machines: Since the assessment of strength requires the use of either weight machines or free weights, the outcome of any experiment comparing the two types of weight training will likely favor the type of training that uses the same type of equipment as the strength measurement. Studies testing strength (one-rep max) using equipment or a type of exercise different from that used in training have found similar gains in strength between weight machines and free weights.

Free Weights: Studies testing strength using equipment that is the same as that used in training have found that there is a greater carryover of strength obtained from free weights to weight machines than the converse and that training with free weights elicits superior strength gains compared to training with weight machines. The superior results of free weight training are likely due to their greater specificity of movement patterns, force application, and velocity of movement.

Advantage: Free Weights

 Workout Flexibility

Weight Machines: Weight machines do not provide much flexibility in designing or performing workouts. For example, while manufacturers of weight machines try to accommodate as many different body sizes as possible, there is still a limit as to how many adjustments can be made in the seat or arm settings, rendering the exercise to be performed in a relatively fixed position. Since each weight machine is designed for a specific exercise, only the intended exercise can be performed with each machine. In addition, training progression is often problematic, as many weight machines are restricted to 10- to 20-pound increments.

Free Weights: As their name implies, free weights do not limit the position of the exercise. Rather, they allow you to make adjustments in position based on your specific biomechanics. Unlike with weight machines, the number of exercises that can be performed with only a couple of dumbbells is nearly unlimited. Since dumbbells and barbell plates come in many different weights, free weights allow for small changes in training load. With free weights, you also have a greater opportunity to engage many large muscles, which means a greater metabolic cost, which can have a greater effect on your fitness and body composition.  

Advantage: Free Weights

 Injury Risk

Weight Machines: Although injuries can occur when using weight machines, they are less likely given weight machines’ fixed positions and guided movements.

            Free Weights: Likely due to their free range of movement, training with free weights presents a greater injury risk compared to training with weight machines. Research has shown that most weight training injuries occur with intense or aggressive free weight training. However, if you focus on performing the exercises correctly or work with a trainer who can monitor your workouts, the risk of injury is no greater than when training with weight machines.

Slight Advantage: Weight Machines

 Overall Winner: Free Weights

Despite the inability to alter their resistance at stronger joint angles and the slightly greater risk of injury, free weights still have the overall strength training advantage because of their training specificity, workout flexibility, and superior stimulus for increasing strength. Possibly the most important reason for using free weights is that, while weight machines allow you to train muscle, free weights allow you to train movement.  

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